MEXICO CITY — As they watched the disaster unfold in New Orleans, Jose Luis Bravo and his fellow average-citizens-turned-rescue-heroes couldn't help remembering the day their own government didn't show up to help them.

At 7:19 a.m. on Sept. 19, 1985, Bravo was preparing for his job as a city bus driver when Mexico City was hit by the largest earthquake in its history. More than 150 buildings collapsed, burying thousands of people, but survivors and relatives were shocked when it took days for any rescue teams to appear.

So they went to work themselves--ragtag teams of young "moles" who dug and dug and risked their lives burrowing into the rubble. They remember that the Mexican army came only to cordon off sites, sometimes preventing the desperate search for buried victims crying for help.

At one point, the rescuers blocked the government from bulldozing the collapsed remains of a hospital where eight newborn babies were later found alive. Some remember an eerie silence from the government of former President Miguel de la Madrid Hurtado for at least 36 hours.

"At the moment we most needed them, they didn't do very well," said Bravo, who dug for three days at the collapsed Nuevo Leon apartment building, where at least 400 people died.

When Mexico City commemorates the 20th anniversary of the terremoto on Monday, its citizens will be grieving for a long list of dead that the government put at 4,500 but which others believe could have been many times that number.

They also will be commemorating the social and political changes in Mexican society that sprang from those horrifying, disorienting, dust-covered, end-of-the-world-like days.

In what still is a very paternal society, the earthquake taught citizens that they could depend on themselves. While there was looting, even by soldiers, many say the outpouring of sympathy, solidarity and voluntarism led to a new consciousness that has fueled neighborhood organizations and a flourishing civil-society movement.

Many trace to those days the beginning of the end of the grip that the long-ruling Institutional Revolutionary Party, or PRI, had on the country. The earthquake response helped galvanize criticism of and opposition to the corrupt government; it is taken as fact now that the PRI managed to win the 1988 presidential election only through massive ballot fraud.

The PRI eventually did fall 12 years later, with the victory of President Vicente Fox.

The 1985 earthquake "had a lot to do with the awakening of people's consciences," said Jose Luis Lezama, an expert in urban studies at the Colegio de Mexico. "It had a lot to do with the rebirth of the democracy in which we are living in Mexico."

Elena Poniatowska, a prominent author who just finished assembling a book of heartbreaking, firsthand accounts of the 1985 victims, says that the pain of those days has been put to good use by the Mexicans.

"It has been transformed into the certainty that Mexicans have the ability to solve their own problems," she told La Jornada newspaper.

Lezama spoke at one of several conferences this week dedicated to the lessons of the earthquake. Participants, including engineers and social anthropologists, have repeatedly referred to similarities between their 1985 experience and the Hurricane Katrina aftermath.

They said that among the positive results in Mexico has been the formation of a government civil-protection system, improvements in building designs, a seismic-alert system, even a system to monitor the nearby Popocatepetl volcano.

Others recalled how, like Hurricane Katrina, the earthquake exposed the unacknowledged rifts and injustices in the society--in Mexico's case, the discovery of a whole network of sewing sweatshops where poor women were crushed and left to die as the owners struggled to recover their machinery.

On the more ominous side, some experts expressed concerns that memories of disasters aren't long enough to prevent recurrences.

Manuel Perlo, an urban affairs expert at National Autonomous University, said he fears that Mexico still hasn't made the leap from reactive mode to preventive mode. He said the country still needs to study its collective memory of 1985 to help prepare itself for the next quake, including a search for documents that officials may have kept hidden at the time.

"Sometimes it's a long time before you can ask important questions," Perlo said. The Hurricane Katrina experience, he said, "gives us a clear lesson that there is no guarantee if we don't do our work correctly."